Doi Takahiro, Tanabe Seiji, Fujita Ichiro
Graduate School of Frontier Biosciences, Osaka University, Toyonaka, Osaka, Japan.
J Vis. 2011 Mar 2;11(3):1. doi: 10.1167/11.3.1.
A fundamental task of the visual system is to infer depth by using binocular disparity. To encode binocular disparity, the visual cortex performs two distinct computations: one detects matched patterns in paired images (matching computation); the other constructs the cross-correlation between the images (correlation computation). How the two computations are used in stereoscopic perception is unclear. We dissociated their contributions in near/far discrimination by varying the magnitude of the disparity across separate sessions. For small disparity (0.03°), subjects performed at chance level to a binocularly opposite-contrast (anti-correlated) random-dot stereogram (RDS) but improved their performance with the proportion of contrast-matched (correlated) dots. For large disparity (0.48°), the direction of perceived depth reversed with an anti-correlated RDS relative to that for a correlated one. Neither reversed nor normal depth was perceived when anti-correlation was applied to half of the dots. We explain the decision process as a weighted average of the two computations, with the relative weight of the correlation computation increasing with the disparity magnitude. We conclude that matching computation dominates fine depth perception, while both computations contribute to coarser depth perception. Thus, stereoscopic depth perception recruits different computations depending on the disparity magnitude.
视觉系统的一项基本任务是通过利用双眼视差来推断深度。为了编码双眼视差，视觉皮层执行两种不同的计算：一种是检测配对图像中的匹配模式（匹配计算）；另一种是构建图像之间的互相关（相关计算）。这两种计算如何用于立体视觉尚不清楚。我们通过在不同的实验环节中改变视差的大小，来区分它们在近/远辨别中的作用。对于小视差（0.03°），受试者对双眼反对比（反相关）随机点立体图（RDS）的表现处于随机水平，但随着对比匹配（相关）点的比例增加，他们的表现有所改善。对于大视差（0.48°），相对于相关的RDS，反相关的RDS所感知到的深度方向发生了反转。当对一半的点应用反相关时，既没有感知到反转深度也没有感知到正常深度。我们将决策过程解释为这两种计算的加权平均值，相关计算的相对权重随着视差大小的增加而增加。我们得出结论，匹配计算主导精细深度感知，而两种计算都对较粗略的深度感知有贡献。因此，立体深度感知根据视差大小采用不同的计算方式。
